Help mounting a large ring to turn.

Discussion in 'Tutorials and Tips' started by Patrick Miller, May 4, 2012.

  1. Patrick Miller

    Patrick Miller

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    I want to turn a segmented ring and need some suggestions on how to mount this to the lathe. The ring consists of 3 layers of 24 segments, each 1/2" thick with a 26"OD and 23" ID total thickness of 1-1/2". I just need to round the outside and inside surfaces- think bicycle tire when it's finished. I have a 26" diameter disc of MDF reinforced and mounted to a face plate that will go on the outboard spindle on my Oneway 1640. The big question is how best to attach the ring to the MDF so it stays put but can be removed with out too much damage to the surface. I am leaning toward the 2-sided tape I got from Craft Supplies, 120+square inches seems like a lot of hold but I've not used this before. Thought I'd ask the forum..
    thanks
     
  2. Thomas Stegall

    Thomas Stegall

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    Considering the fource generated by something spinning of that diameter I seriously doubt that tape would hold it, and it would be dangerous and disasterous if the tape failed. My suggestion would be to cut 12 pieces on a bandsaw that match the outside contour of the ring and screw them into a faceplate to hold the ring while you turn the inside. Then cut pieces to match the newly shapped contour of the inside of the ring, mount the pieces and turn the outside of the ring. If you planned on doing more of these in the future I would suggest turning a disc with a recess on the edge so that the inside of the ring could be turned first to disc recess diameter. The disc recess would overlap the inside edge of the ring. The disc could then be screwed into the faceplate sandwiching the ring between the disc and faceplate while you turn the outside surface.

    Tips; 1) mark the holding pieces with paint or marker so they stand out visually when the lathe is turned on so you don't cut them, and so they don't cut you. 2)Put something as a thin padding between the holding pieces and your ring to absorb/prevent vibration and/or movement. 3) Before you begin, turn the faceplate so the face is absolutely true and then mark rings with a pencil to help you center your ring perfectly on the faceplate. And, wear a face shield. :) Good luck!
     
    Last edited: May 4, 2012
  3. Patrick Miller

    Patrick Miller

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    Thanks Thomas-
    Glad I asked. Your suggestion hadn't occurred to me and it seems like a much safer plan. I will remake my mounting plate to allow the keeper blocks on the outer circumference. MDF is much cheaper than a trip to the ER.......
     
  4. john lucas

    john lucas

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    Hot glue but put it on the outside surface of the ring. I just did something similar only smaller, I think it was about 15". The first one flew off when I got up to cleaning up speed. When I put the hot glue on the joint between the outside surface the the mdf it held. I guess it needed some sort of stop to keep the force from throwing it out.
    MDF isn't the best surface for glue or tape. It tends to peel away a layer at a time. If you have some plywood use that.
     
  5. Patrick Miller

    Patrick Miller

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    thanks John
     
  6. john lucas

    john lucas

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    I hope I explained that clear enough. I had to run out the door to a photo assignment. Put some glue on the back of the ring and glue it down to the backer board. then take the hot glue and run a ring around the outside of the ring where it touches the backer board. This is where the strength comes in I found. It will often peel off fairly well when your done but if not I use a piece of guitar string tied to 2 sticks to sort of saw through the glue. That's worked really well for me to separate the ring from the backing plate.
     
  7. Joe Greiner

    Joe Greiner

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    I would favor mechanical connections vs. chemical.

    As I read your brief, your objective is a large donut nominally 26" outside diameter, with body of 1 1/2", less turning allowances; say 1 3/8" body and 25 7/8" final OD.

    On similar work, I've made the first ring of segments about 1" or so wider than its brothers. Attach with screws in this waste area to a plywood disk, radius slightly less than the mid-point of the donut body, e.g. 24" OD in your case.

    Turn the outside profile of the donut, to the edge of the plywood disk on one side, and full width on the other.

    Attach several (more = better) bent metal brackets to the disk to reach past the outside of the donut, with cushioning and spacers to assist centering. Wrap the brackets with a very large hose clamp assembled from many smaller ones, to clamp the work. Flip the piece to cut off the wider ring and shape that region of the donut. Flip again to shape the region on the other side.


    An interesting alternate to the wider ring for the first turning would be to make the disk flush with the inside ring. Place screws in the interface so that they engage both the disk and the ring, half in each. This is an extremely robust connection, sometimes used in large steam engines and pressure vessels. The final turning would remove the "footprints" of the screw threads, and might be applicable if you've already cut your segments. In fact, upon reflection, the first turning could shape all except that quadrant of the donut body.

    And upon further reflection, the first turning of the other process could also incorporate its third step.
     
  8. Gil Jones

    Gil Jones

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    Attach Ring

    My donut chuck drive plate is 20" diameter. Attach (with screws and/or wood glue) your ring to an appropriately sized circle of 1/2"+ plywood, and attach that (mechanically) to the donut chuck drive plate.
    Gil
     
  9. Dick Sowa

    Dick Sowa

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    If you are turning this ring prior to mounting it onto a segmented vessel, then a bead of hot melt glue around the perimeter of the assembled ring will be plenty. Especially if you are merely flattening the face and rounding the corners of the segments, prior to attaching to the larger vessel. I use hot melt with MDF for rings like that all the time, and have never had one fail. But I am not hogging off wood either...just flattening the faces and knocking the corners off to make it round.

    For what it is worth, I never finish the inside of the ring, or even touch it with a tool, until it is mounted to the vessel. Then I have more meat to play with, and help refine the shape of the vessel.
     
  10. Patrick Miller

    Patrick Miller

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    thanks

    Thanks again to all for the help and suggestions- 2+ heads are certainly better than one. Here is what I did- I used a bit of the 2-sided tape to hold the donut in position on my mounting plate then added a dozen or so spring clamps. Then I mounted a router in a floor mounted tool rest stand and finished the inside diameter using the lathe simply as a jig. I then cut a number of blocks with a curve that matched the ID and fastened them to the mounting disc and snug to the ID with a piece of 3/8" plywood on the block extending past the ring by 1/2" to clamp the ring in place. I then turned (with the lathe and a gouge) the OD true, rounded over the edge facing me and turned a decorative cove centered on the circumference. I then flipped the ring over and finished the opposite side. No screaming projectiles or trips to the ER and I got the piece I was looking for!
    thanks again-
     

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